1. Field of the Invention
The present invention relates to an apparatus and method to actively reduce the magnitude of undesirable vibrations in a rotating roll. More particularly, the present invention relates to an apparatus and method to actively reduce undesirable vibration in a device for the treatment of a material web, specifically a paper or cardboard material web.
2. Description of the Related Art
A device to actively reduce the magnitude of undesirable vibrations in a rotating roll is described, for example, in German patent document no. DE 196 52 769 A1. In accordance with a first design alternative described therein, a vibration sensor is located at one bearing position, or at the bearing positions of the roll. In accordance with a second design alternative described in German Patent document no. DE 196 52 769 A1, it is suggested to locate the vibration sensor at the machine center. In an experimental arrangement, a capacitive sensor was located in the machine center, i.e., in the area of the longitudinal roll center, close to the substantially circular cylindrical roll shell. Positioning the vibration sensor in the area of the machine center offers the advantage that the amplitude of vibrations of a roll can be accurately measured due to the substantial distance of the sensor from the bearing positions of the roll, and from the significant xe2x80x9cswingsxe2x80x9d of the roll resulting from the substantial distance separating the roll bearings (for example due to additional deflection vibration contributions). It is, however, a disadvantage that the capacitive sensor must be located in close proximity to the roll surface.
When utilizing the vibration weakening device in a machine for the production and/or coating of a material web, specifically a paper or cardboard web, there is an inherent risk of damage to the sensor in the event of a web break and the subsequently resulting xe2x80x9cwrap-upxe2x80x9d of the roll. There is also the danger that the ability of the sensor to function may be impaired due to contamination from coating medium, fiber components, etc. In addition, a sensor located in immediate proximity to the shell surface of the roll makes access to the roll shell more difficult for maintenance or operating personnel. It has, after all, proven difficult to precisely measure the vibration amplitude on coated surfaces, for example rubber coated surfaces and/or surfaces covered with a layer of coating medium.
Sensors which are located at the bearing positions of the roll do not exhibit the aforementioned disadvantages. However, due to the fact that the bearing positions coincide with the nodal points of the undesirable roll vibrations, it is considerably more difficult to measure the vibration amplitudes with the necessary precision at the bearing/mounting positions than it is in the area of the machine center.
Patent document no. WO 97/03832 describes a process and a device for the reduction of deflection vibrations in rotating systems which are designed for utilization with impression cylinders in rotogravure presses. However, the working width and running speed of material webs in rotogravure presses of this type are considerably different from that in a machine for the production and/or coating of material webs.
The present invention provides a method and apparatus that enable precise detection and measurement of the roll vibration amplitudes and is not susceptible to contamination and damage, and permits unhampered access to the shell surface of the roll by operating and/or maintenance personnel. A sensor arrangement having at least one sensor is located radially inside the substantially circular cylindrical outer shell surface of the roll relative to the rotational axis of the roll and/or at least one sensor is located remotely from the substantially circular cylindrical shell surface of the roll. The sensor arrangement measures the undesirable vibrations. A power unit device influences, dependent upon the measuring result, the roll in order to reduce the undesirable vibration. The apparatus and method of the present invention are intended for utilization in machinery for the production and/or treating of, and particularly for applying a coating to, a material web, specifically a paper or cardboard web.
A sensor device is located under the roll surface. In this location it is neither at risk from contamination through exposure to coating material, nor is the sensor device at risk of damage due to a web break. In addition, with the sensor located under the roll surface, free access to the roll surface is assured. Further, a sensor device is located in the area of the machine center, i.e., in the area of the longitudinal center of the roll, thereby enabling a high precision measurement of the amplitude of the roll vibration.
The sensor device includes at least one compression and/or tension sensitive element such as, for example, a wire strain gauge. Sensor elements of this type have proven themselves rugged, reliable and precise especially when applied for the purpose of detecting/measuring mechanical stress conditions. The compression and/or tension sensitive element may, for example, be located on the inside surface of the roll cylinder where it is protected by the roll shell (which may, for example, be manufactured from steel) from exterior influences caused by, for example, a web break. In the instance of internally cooled rolls, it must be ensured that the compression and/or tension sensitive element is resistant to the cooling medium, for example, water. In addition, or as an alternative, a compression and/or tension sensitive element is located on the outside surface of the roll cylinder underneath the roll surface cover layer which is, for example, formed of a protective layer of rubber, rubber-type material, synthetic material or other similar material. In such an arrangement, the compression and/or tension sensitive element is protected from exterior influences by the protective roll cover/layer. More particularly, the compression and/or tension sensitive element is protected from damage in the event of a web break and from contamination through exposure to coating medium when located under the protective roll cover/layer.
A sensor device is also located remotely from the roll surface. The distance between the sensor device and the roll surface is selected so that the sensor device is neither contaminated through exposure to coating medium splashes, nor damaged in the event of a web break. In addition, unhampered access to the roll surface is assured due to the distance between the sensor device and the roll surface. Again, location of the sensor device in the area of the machine center ensures precise detection/measurement of the roll vibration amplitude. In a machine equipped with two rolls which together form a xe2x80x9cnipxe2x80x9d through which the material web travels, signals can be detected/measured particularly effectively by placing a sensor device in the connecting plane of the axes of the two rolls. Remote vibration detection/measurement is provided simply and reliably by a sensor device that includes at least one optical sensor unit. In order to ensure free access to the shell surface of the roll, it is advantageous to locate the optical sensor unit at a distance of at least one meter from the roll surface.
Sensor units based on various principles of measurement can be utilized. The optical sensor device may, for example, be a laser-vibrometer, which may be purchased, for example, under the identification VH 300 from Ometron, Inc., Dulles, USA. This laser-vibrometer detects/measures the vibration of the roll as the component of the speed of the surface of the rotating roll that is progressing parallel to the laser bean conducting the measurement. In addition, or as an alternative, the sensor device can include an interferometrically operating sensor device that detects/measures mechanical tension/stress conditions of the roll surface. Such interferometric sensor devices are used in the area of non-destructive materials analysis. The interferometric sensor device detects/measures the mechanical tension/stress conditions, for example, at the substantially circular cylindrical shell surface of the roll.
In addition, or as an alternative, the interferometric sensor device measures the mechanical tension/stress conditions in the area of a header section of the roll, in which the roll surface tapers from the substantially circular cylindrical shell surface to the roll journals. The changes in the surface tension/stress of the roll caused by undesirable vibrations are especially pronounced and distinct in the transition area between the shell surface and the header section, as well as in the transition area between the header section and the roll journal. Measuring the mechanical tension/stress conditions of the roll in the area of the header section has the additional advantage that the interferometric sensor device may be located prior to, or after, the roll, viewed in direction of the roll axis, thereby not hampering free access to the shell surface of the roll. The tension/stress conditions in the header area may, however, also be detected/measured by other suitable sensors such as, for example, wire strain gauges.
The present invention also includes a control unit which, based on the detected/measured signals of the sensor device, determines actuating signals for the power unit device. The control unit, for the purpose of determining the actuating signals, combines the measured signals from a multitude of sensors additively and/or subractively and/or weighted and/or averaged and/or phase corrected. This allows for consideration of peculiarities in the vibration characteristics of the roll, depending upon prevailing operating parameters, and peculiarities of the utilized sensor devices, specifically with regard to their sensitivity to certain ranges of vibration frequencies. The control unit also considers the measured signals of at least one sensor device located at the bearings of the roll such as, for example, a compression and/or tension sensitive element, an acceleration sensor (for measuring radial accelerations), or the like.
In addition, the present invention provides a method to actively weaken undesirable vibrations of a rotating roll. The undesirable vibrations are detected/measured by use of a sensor. A power unit device influencing the roll is triggered dependent upon the detected/measured results, thereby weakening the undesirable vibrations.
As used herein, the terminology xe2x80x9cin the area of the machine centerxe2x80x9d refers to a relatively wide area around the exact longitudinal center of the roll. The reason for this is that, in a good first approximation and with consideration of occurring centrifugal forces, the deformation of the roll due to vibration follows a parabola that progresses between the two side bearing positions and is substantially symmetric about the machine center. The value of a parabola changes only slightly in the maximum range. Thus, with regard to the precision of the measurement of the vibration swings of the roll, the xe2x80x9carea of the machine centerxe2x80x9d can, therefore, be defined as the area between the two points in axis direction of the roll in which the vibration swing is approximately 75% of the maximum swing in the exact machine center.